While higher performance vehicles have come into being in recent years, there have been developed various apparatuses for detecting the rotation angle of the steering wheel (hereinafter called SWH) with use of rotation angle detectors (hereinafter called RAD) for performing various types of control.
One of such conventional rotation angle detectors will be described with reference to FIG. 4, FIG. 5A and FIG. 5B.
FIG. 4 is a perspective view of a main portion of the conventional RAD and FIG. 5A and FIG. 5B are voltage waveforms obtained from the RAD. Rotating member 1 in a disk form has, in its center, engagement portion 1A engaging a shaft (not shown) of an SWH inserted therein and opening portion 1C allowing the shaft of the SWH to pass therethrough. On the circumference of rotating member 1, there are provided a plurality of through holes 1B at a predetermined pitch. Across through hole 1B formed in rotating member 1, there are arranged photo-interrupters 2, 3, each made up of a light emitting element and a photo sensing element opposing each other. Further, the photo-interrupters are held by holding member 4 in predetermined positions slightly offset with respect to through hole 1B, so that detection signals output therefrom while rotating member 1 rotates may have a predetermined phase difference therebetween.
Further, there are disposed wiring board 5 with a plurality of wiring patterns (not shown) formed on both sides thereof and a control unit (not shown) made of a microcomputer and the like. By having photo-interrupters 2, 3 connected to the control unit, the RAD is constructed.
In the described configuration, rotating member 1 is rotated according as the SWH is rotated and, thereby, admission of light and cut-out of light are repeated.
As a result, detection signals in which periodical rectangular waveforms with a phase difference therebetween, as shown in FIGS. 5A and 5B, continue are output from photo-interrupters 2, 3 to the control unit.
The rotation angle of rotating member 1 is detected by counting the number of waveforms in either of the detection signals from photo-interrupters 2, 3. The rotating direction can also be detected as follows. When, for example, the waveform of photo-interrupter 2 shown in FIG. 5A is lagging behind the waveform of photo-interrupter 3 shown in FIG. 5B, it is determined that the rotation is in a clockwise direction, and, when in reverse the waveform of photo-interrupter 2 is output faster than the waveform of photo-interrupter 3, it is determined that the rotation is in a counterclockwise direction. An example of RAD having the described configuration is disclosed in U.S. Pat. No. 6,380,536.
At this time, if the pitch of through hole 1B of rotating member 1 is set at 6°, the width of the hole set at 3°, and the phase difference between photo-interrupters 2, 3 set at ¼ period, waveforms of FIG. 5A and FIG. 5B each become a waveform having a period of 6° and they become ¼ period shifted from each other. Thus, a RAD capable of detecting a rotation angle down to as small an increment as 6°/4=1.5°, i.e., that having a resolution of 1.5°, can be structured.
The described conventional RAD detects a rotation angle with use of two sets of photo-interrupters 2, 3, as well as rotating member 1 provided with a plurality of through holes 1B formed therein. Therefore, there arises such a problem that layout and machining of the components become complicated and costly. Further, since there are limits in reducing the pitch distance between through holes 1B and the width of the hole, it is difficult to perform angle detection with a high resolution.
The present invention addresses the above mentioned problems in the prior art and, accordingly, it aims at the provision of a RAD capable of angle detection at a high resolution with a simple structure.